A quantum dot light-emitting diode (QLED) is a light-emitting diode in which quantum dots (QDs) are directly activated by a current to emit light. The QLED has advantages of a quantum dot material. For example, the light emitted by the QLED has a tunable wavelength and a narrow linewidth (15-30 nm). The QLED has a high efficiency (70%-100%), excellent photo, heat and chemical stability, and is compatible with film forming processes for an OLED (organic light-emitting diode). These advantages make the QLED to be potentially applied to the new generation of flat panel display with high color quality and low power consumption, and thus have drawn increasingly more attention. However, by taking a red QLED as an example, the red QLED has an external quantum efficiency (EQE) up to 20.5%, a maximum brightness >104 cd/m2, and a lifetime up to 10 Wh (T50@100 cd/m2). This still falls behind the performance of OLEDs in mass production, and does not meet requirements of commercialized products.
Currently, in a conventional organic-inorganic hybrid QLED device, a quantum dot light emitting layer is interposed between an organic hole transporting layer and an inorganic electron transporting layer to form a sandwich structure. The inorganic electron transporting material usually adopts a film comprising ZnO nano-particles which has a high electron mobility (10−3 cm2V−1S−1), for facilitating electron injecting and transporting. The organic hole transporting material has a HOMO in a range of −5.0-6.0 eV, and the quantum dot has a valence band in a range of −6.0-7.0 eV, which indicates there is a large hole injecting barrier therebetween. Furthermore, most organic hole transporting materials have a mobility <10−4 cm2V−1S−1, which is nor favorable for hole injecting and transporting in the device. This will lead to an unbalance between electron injecting and hole injecting in the device, and energy will be consumed in the form of heat.